Assicwob- to automatic electbic



' A B. SMITH. I

AUTOMATIC TELEPHONE SYSTEM".

APPLICATION FILED MAY l0. ms.

1,315,441. PatentedSept. 9,1919. ya 7SHEETS-SHEETI.

A. B. SMITH.

AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED MAY 10. 1916.

1 ,3 1 5 414: 1 Patented Sept. 9, 1919.

A. B. SMITH AUTOMATIC TELEPHONE SYSTEM. APPLICATION 'HL ED MAY 10. 1915.

1 ,8 1 5,441 Patented Sept. 9, 1919.

' I 7 $HEET$$HEET 3- A. B. SMITH.

AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED MAY 10. 1916.

.1 3 1 5 44 1 PatentedS ept. 9, 1919.

7 SHEETS-SHEET A. B. SMITH. AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED MAY 10, I916.

Patented Sept. 9, 1919.

7 SHEET HEET Fi 5H.

A. B. SMITH. AUTOMATlC TELEPHONE SYSTEM.

APPLICATION FILED MAY 10. 1916. C 1 ,315,4%1 PatentedSept. J, 1919.

T SHEETSSHEET 6- A. B. SMITH.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED MAY 10. 1916.

1,315,441. Patented Sept. 9, 1919.

7 SHEETS-SHEET 7.

HZZUI may ARTHUR IBESSEY SMITH, 01F EVANSTON, ILLINOIS, ASSIGNOR T0AUTOMATIC ELECTRIC COMPANY, A CORPORATION OF ILLINOIS.

Specification of Letters Patent;

Patented Sept. 9, 1919.

Application filed May 10, 1916. Seria1 No.'96,494.

To all whom it may concern Be it known that I, ARTHUR BnssnY SMITH, acitizen of the United States of America, and a resident of Evanston,county of Cook, and State of Illinois, have invented certain new anduseful Improvements in Automatic Telephone Systems, of which thefollowing is a specification.

While my invention relates ingeneral to automatic telephone systems, itis concerned chiefly with such systems as comprise a plurality ofexchanges interconnected bytoll or long distance lines, and hasparticular reference to methods of automatic calling over toll linesupon which phantom circuits are superimposed. r

It is well known that in order to maintain quiet operation of a phantomcircuit, all disturbancesor current changes in one physical lin whichare not-compensated for by corresponding changes in the other physicallinemust. be eliminated; or, in other words, the two physical circuitsupon which the phantom is superimposed must be balanced in order toprevent current flow from one physical to the other via the phantom.Such conditions are difficult if not impossible of" attainment where thephysical circuits are used separately as controlling circuitsforautomatic switches.

My pending application, Serial No; 86,596, discloses a. system ofautomatic calling'over phantome-d toll lines in which therequisiteconditions for quiet operation are obtained, and in which automaticconnections may be established over any two of the circuits in eitherdirection. It is desirable, however, to be able to use all three of thecircuits for automatic connections in either direction at the same time.

The principal object of the present in ventioh is to provide a new andefiicient method of automatic calling over toll lines havingsuperimposed phantom circuits, whereby connections may be establishedantomatically over the physical circuits or over the phantom circuitswithout interference.

In carrying out my invention in connece tion with two toll lines havinga superimposed phantom circuit, I employ preferably a so-called simplexoperating circuit super-- imposed on the phantom circuit in well knownmanner; and, in addition, I employ alternating currents of differentfrequencies adapted to be separately or simultaneously included in theoperating circuit, together with suitable alternating current relayseach of which is soconstructed, or has its local circuit so arranged,that it will respond only to current of a. certain frequency.

Several son'icwhat dlfi'erent circuit ar raugements are available inaccomplishing the foregoing general results, the two which I considerthe most useful and practicable being illustrated and describedhereinafter,

reference being had to the accompanying drawings.

For a clear'understanding of the drawings, Figures 1, 2 and 3 should bearranged in order with the lines at the sides thereof in alinement, Fig.4 should be joined at its left hand end to the lower right hand cornerof Fig. 3, and Fig. 5 should be placed as a continuation of Fig. 4. Theapparatus shown in Figs. 1 and 2 is located in what I shall hereinafterdesignate as the. No. 1 exchange, while the apparatus shown in Figs. 3,4, and 5 is located in what I shall hereinafter designate as the No. 2exchange. Figs. 2 and 3 illustrate an alternative method of carrying outmy invention which will be described later on.

When the drawings are properly laid out and joined together it will beseen that I have shown a toll line 10 1102 extending from'jack J 2 inthe No.. 1 exchange to jack J in the No. 2 exchange; a second toll lineextending from Jack J 4 in the No. 1 exchange to jack J 7 in the No, 2exchange; and a phantom circuit superimposed in the reg ular manner uponthe said toll lines and extending from jack J 3 in the No. 1 exchange tojack J 6 in the No. 2 exchange.

It will be shown hereinafterthat all three of the above lines areadapted for manual as well as automatic operation in both directions, ashas been previously mentioned. In accomplishing the latter operation Iemploy, as before stated, a so-called simplex circuit superimposed onthe phantom circuit in an obvious manner and evidently terminating turnterminate in three groups of apparatus indicated, respectively, byreference characters M M and M and which, in the case "of the No. 2exchange, terminate in three similar groups of apparatus indicated,respectively, by reference characters M M, and'M The apparatus M ,.Metc, com-.

prises the means peculiar to my invention and will be fully describedhereinafter.

To better facilitate the understanding of my invention I have elected toshow a part of the apparatus in operated position where by a completecircuit connection has been established between a calling substation A(Fig. 1) and a called substation A (Fig. 5). The said connection hasbeen established through the medium of multiple jack J, cord circuit P,jack J repeating coil R toll line 103104, repeating coil R, repeater E,selector switch F, and connector switch H.

The substation A (Fig. 1) may be of any suitable type or constructionsuch, for example, as the type disclosed in British patent to T. GMartin, No. 1410 of 1010. As shown herein it comprises essentially thereceiver 2, transmitter 3, switch book 4, ringer 5 and condenser (3.Being an automatic substation there is also provided a pair of impulsesprings 7 and 8 controlled by the impulse wheel 0 through the medium ofa finger hole dial (not shown).

The line conductors 12 and 13 of the substation A are connected at theNo. 1 exchange to the individual line switch C which may be of thegeneral type of line switch disclosed in British patent to R. \V. James,No. 20,301 of 1000; being, however, of the particular type shown inUnited States Letters Patent No. 1,078,090, granted Jan. 17, 1912, toFranl; Newforth. Since line switches of the above type are well knownand form no part of my invention an extended description will not begiven. It will suflice to say here that'through the medium of lineswitch C'the line of substation A is given access to a plurality ofselector switches (not shown) which may be similar to the selectorswitch F to be mentioned hereinafter. trunk line which may be extendedto one of these selector switches is indicated by reference characters17, 18, and 19.

In additionto the line switch (1' there is also provided for the line ofsubstation A a multiple ack J, which, as shown herein, is directlyaccessible to the toll operator. It is to be understood, however, thatthe toll operator may complete connection 10- cally by any other knownmethod, the method shown having been chosen principally on account ofits simplicity.

At P I have shown a toll operators cord circuit which may be of anysuitable type or construction. As shown herein, it comprises among otherdetails a bridged relay 36, which, in conjunction with sleeve relay 35,controls the supervisory lamp L; and the ringing up locking relay 37which, in conjunction with sleeve relay 38, controls the supervisorylamp L. Keys K and K are ringing keys, while key K is a listening Athree conductorkey, adapted, when operated, to bridge the operators headset across the two strands of the cord circuit.

The toll operator, besides having access to the local subscribers lines,has before her multiple jacks which are terminals of toll linesextending to other exchan es. The three jacks shown at the right of lig. 1, that is, jacks J J, and J, are associated with toll linesextending to the No. 2 exchange, as has been previously stated. For eachof these lines, including the phantom line, there is provided a group ofapparatus, which in the case of the toll line 103-l(H is indicated as awhole by the reference character M". Considering the apparatus M more indetail, reference characters 02 and 50 indicate, respectively, a dropand cut-off relay. Reference characters and 52 indicate, respectivel y,an A. C. generator and a A. (J. relay. The A. C. relay 52, it will beobserved, has its two windings connected in parallel with a condenserinseries with one of the windings in order to throw the currents in thetwo windings out of phase. Relay 51 is initially controlled by the key Kand is adapted, when energized, to substitute the generator 80 for therelay 52 in the operating circuit associated with toll line 103104 whichwill be more fully described hereinafter. The key K also serves toinsert the calling device S in this operating circuit, whereby impulsesmay be transmitted to the distant exchange. The calling device S may beof any suitable type, it being only required that the impulses producedin its operation shall cousist of interruptions of the circuit in whichit is included. Such a calling device is shown in British patent to S.G. S. Dicker, No. 29,051 of 1910. The calling device S is notnecessarily individual to the toll line 103104, but there may be onecalling device for each operator. The reactance coil 57 and thecondenser 50 constitute what I term a barrier and have a certainparticular value of inductance and capacity depending on the frequencyof current to which the associated A. C. relay 52 is adapted to respondas will be fully explained hereinafter.

A slight inspection of Figs. 2 and 3 will now show that the severalgroups of appara tus M M M, M, and M are each substantially like thegroup of apparatus .\l just described. Referring to the group ofapparatus M (Fig. 3), a six conductor trunk line indicated by referencecharacter 110 may be seen extending upward and to the right, where itterminates in the repeater E (Fig. 4). The trunk lines 105, 107, 100.100. and 108, associated, respectively. with the groups of apparatus M Metc, are assumed to extend to similar repeaters, one

of these repeaters being in fact shown at E (Fig. 1).

While, as has been stated, the various sets of equipment ME M etc., areall substantially alike, this is strictly true only in so far as ei'uipmcnt at opposite ends of a particular line is concerned. For example,the apparatus shown at M may be exactly like that shown at M. Theequipment M however, with the identical equipment M, and the equipment Mwith the identical equipment M", differ radically from equipment M inelectrical characteristics, and these differences constitute the chieffeature of my inveution. Briefly, the A. C. generators S0 and 180deliver current of a frequency which is preferably somewhat higher thanthe highest commercial power frequency; A. C. generators 81 and 181deliver current of a higher frequency than that delivered by generators80 and 180; while generators 82 and 182 deliver current of a stillhigher frequency. I

sponding to any currents except those of the.

proper frequency can best be explained in connection with the detaileddescription of the operation.

Proceeding now with the description of the automatic apparatus, therepeater E may be of the general type of repeater disclosed in U. S.Letters Patent No. 1,136,912, granted April 20, 1915, to Talbot G.Martin, although the circuits are modified some-i what to enable therepeater to operate in conjunction with the equipment shown at M (Fig.3). The operation and functions of the various relays of the repeaterwill be described fully in the detailed specification.

Directly connected with the repeater E is shown a. selector switch F,which may be of the general type of selector switch disclosed in U. S.Letters Patent No. 815,321, granted March 18, 1906, to Keith, Erickson,and Erickson; being, however, of the particular type disclosed inBritish patent to the Automatic Telephone Mfg. (10., No. 2,543 of 1914.Such a selector switch, as is well known, may be operated in response tothe first digit of a called number to select one of a number of groupsinto which the lines of the No. 2 exchange are divided. For this purposethe selector F may be given access to a number of groups of trunk lines,the trunk lines of each group being extended to a group of connectorswitches. 7

One of these trunk lines is shown as extending to the connector H (Fig.5), which may be of the general type of' connector switch disclosed inU. S. Letters Patent No.

815,176, granted March 13, 1906,..to Keith,

more nearly of the particular type disclosed in British patent to theAutomatic Telephone Mfg. Co, No. 2,270 of 1914. The connector switch Hhas access to a single group of subscribers lines and may be operated inresponse to the last two digits in a called number to completeconnection to a wanted line in the group.

One of the lines accessible to the connector H, comprising theconductors 12 and 13, is shown extending to the substation A, which maybe similar to substation A (Fig. 1) already described. The line ofsubstation A is provided at the No. 2 exchange with an individual lineswitch C which may be similar to the line switch C (Fig. 1). Conductors1 1, 15, and 16 are assumed to extend to multiple jacks by which tolloperators in the No. 2 exchange may be given access to the line ofsubstation A.

While I have shown throughout the drawings a plurality of batteries, itis to be unvderstood that there are preferably but two of. thesebatteries, one for each exchange, and each having its positive polegrounded; Associated with the connector H I have shown a generator Genfor supplying ringingcurrent, an interrupter I for supplyingintermittent ringing impulses, and a busy signaling machine Q.

Having given a general description of the apparatus, I will now proceedto a more detailed explanation of the operation of the same. Inasmuch asa great deal of the automatic equipment shown here is Well known andhasbeen described fully in the publications previously referred to, theoperation of such apparatus will be described in a more or less generalmanner. I will first describe the operations which take place whenestablishing the complete connect-ion previously referred to between thesubstation A (Fig. 1) and the substation A (Fig. 5). The call is assumedto have originated with the subscriber at substation A and theconnection is therefore handled by an op erator in the No. 1 exchange.

Referring now to Fig. l, the subscriber at substation A, in initiating along distance call, must first get into communication with a so-calledrecording operator at the No. 1 exchange. Any approved method ofaccomplishing this object-will serve, but since the substation A is anautomatic substation, it will be assumed that the operator has beencalled automatically as follows: Upon removing the receiver atsubstation A, the line switch C is operated to extend the lineconductors 12 and 13 through to a selector switch, which may be theselector to which the trunk conductors 17, 18, and 19extend. After theline switch has operated, the calling subscriber may manipulate thefinger hole dial of his instrument, thereby operating the selectorswitch to select a group of trunks extending to recording operat'orspositions; after which the selector operates antomatically to connectwith an idle one of these trunks, all in a well known manner, as shown,for example, in the co-pending application of Talbot G. Martin, SerialNo. 570,165, filed July 5, 1910. The calling subscriber upon hearing theoperator respond, will give her the necessary information, such asthename and address of the person with whom conversation is desired, andalso his own name and telephone number, and will then replacehisreceiver, thereby restoring his line switch and the selector switchto normal position. The recording operator in the meantime has writtenout the data received from the calling subscriber on a ticket, which ispassed to a toll operator whose duty it is to complete the requiredconnection.

In the case under consideration the wanted subscriber is located in theNo. 2 exchange. The toll operator, therefore, having first tested thesleeve of jack J with the tip of her plug to determine its idle or busycondition and having found it idle, will insert, the calling plug ofcord circuit P therein, thereby completing the following circuit; groundat G, winding of cut-off relay 50, conductor '71, contact springs 72 and73 of repeater E, conductor 70, sleeve of jack J sleeve of plug, andwinding of relay 38 to battery ll. Relay 38, upon energizing, extendground to the armature of relay 37 and also disconnects the busy testconductor 21, from the upper strand of the cord circuit. The cut-oilrelay 50. upon energizing, disconnects the drop '62 and the lineconductors extending to repeater E from the tip and ring conductors ofjack J in an obvious manner and in addition prepares a locking circuitfor relay 51 which will be referred to later.

Since the connection is to be established automatically, the operatorwill now throw the calling device key K thereby inserting the callingdevice S in a circuit to be described presently, and at the same timecompleting a circuit for relay 51 as follows: ground at G contactsprings 74 and 75, and winding of relay 51 to battery B. Relay 51,uponenergizing, completes a locking circuit for itself over thefollowing path: ground at G contact springs 69 and 68, contact springs63 and 64, and winding of relay 51 to battery B. As a further result ofthe energization of relay 51, contact spring 66 is separated fromcontact spring 67 and i shifted instead into engagement with contactspring 65, whereby is completed an operating circuit for the A. C. relay.152 at the distant exchange as follows: ground at G A. C. generator 80,non-inductive resistance 55, calling device S,contact springs 76 and 77contact springs 65 and 66, reactance coil 57,

condenser 56, conductor 90, windings 113 and 1-1-1 of repeating coil Rin parallel, winding 111, 112, 115, and 116 of repeating coils 1t and Rin parallel, toll lines 101-102 and 103-401 in parallel, windings 1'17,118, 121, and 122 of repeating coils R and R in parallel, windings 119and 120 of repeating co l R in parallel, conductor 190, condenser 156,reactance coil 157, contact springs 196 and 167, and windings of A. C.relay 152 to ground at G. The reactance coils 57 and 157 and thecondensers 5(3 and 156 are of such inductance and capacity,respectively, that the above circuit is resonant to the frequency ofgenerator 80, whereby sufiicicnt current is permitted to flow to operatethe A. t. relay 152. It will be observed that in addition to the path toground by way of conductor 199, the e are four other possible paths toground by way of which current from generator 80 might find its way backto ground at (1. These alternative or shunt paths may be easily tracedby way of conductors 91 and 92 (Fig. 2) and 191 and 192 (Fig. 3). Eachof these conductors is in series with a barrier comprising a reactaucecoil and condenser similar to reactance coil 57 and condenser 56. Thebarriers in series with conductors 91 and 191 are tuned together withreference to the frequency of generator 81; while the barriers in serieswith conductors 82 and 182 are tuned together with reference to thefrequency of generator 82. It will be clear from the foregoing thatresonance will not, occur in any of the branch paths when in series withgenerator 80 and the barrier included in conductor 90, whence it followsthat practically all the current flow is confined to the path traced viathe A. C. relay 152. It follows, therefore, that while A. C. relay 152is operated, the remaining A. C. relays 6., relays 53, 51, 153, and 154receive Ver little current and do not respond.

lVhile the various barriers are themselves amply suflicient to directthe alternating current delivered 'by the several generators into theproper paths to operate the proper relays, it is possible to increasethe sensibility of the relays somewhat by adjusting the local circuit ofeach relay with respect to the frequency on which the relay is intendedto 0perate. For example, considering relay 152, the closed loopcomprising the two windings and the condenser in series should beresonant to the frequency of generator 80.

To proceed with the operation, the A. C. relay 152, upon attracting itsarmature, completes a circuit including the line relays of repeater E(Fig. 4) over the following path: ground at G, winding of relay 211,conductor 179, contact springs 185 and 186, winding 123 of repeatingcoil R contact and armature of A. C. relay 152, winding 124 of repeatingcoil R contact springs 187,

188, and 189, conductor 178, and winding of 239. In this manner aguarding potential is,

relay 210 to battery B Upon energizing,

relay 210 closes a circuit for the slow. acting relay 213 as follows:ground at G flcontact V springs 217 and 218, and winding of relay 213 tobattery 13*. Relay 213 attracts its armature, and by means of contactsprings 232, 233, and 234 shifts the sleeve ofjack J from its normalconnection by way'of conductors 170 and 171 to relay 150, to battery Bby way of conductor 170 and resistance placed on the sleeve of jack Jand, furthermore, should an operator disregard her busy test or pluginto jack J accidentally I she will not release a connection alreadyestablished automatically for the cut-ofl re-. lay 150 has had itscircuit opened as explained. Relay 213 also prepares, by means ofcontact springs 237 and 238, an energizing circuit forrelay 214; and, bymeans of contact springs 235 and 236, a locking circuit for relay 212. i

Relay 211, upon energizing, closes a circuit for the line relay 250 ofthe selector F over the following path: ground at G",

lower winding of line relay 250, normally closed contacts of relay 253,conductor 243, contact springs 220 and 219, contact springs 230 and 231,winding of reactance coil 215, conductor 240,contact springs 226-and225,

conductor 242, normally closed. contacts of relay 253, and upper windingofline relay 250 to battery 13. The line relay-250 energizes over theforegoing circuit and thereby closes an energizingcircuit from ground atG for the slow acting relay 251, which relay, upon energizing in turn,prepares circults 1n the well known manner for, the 7 vertical androtary magnets 255 and 256.

The operator at the No. 1 exchange'may now proceed to dial the wantednumben.

Upon the operation of the calling device S in accordance with the firstdigit, the impulse springs of the calling device are separatedmomentarily a number of times interrupting each time the previouslydescribed circuit including the generator 80 and the A. C. relay 152. Asa result of these 6' interruptions of its circuit, relay 152 de3energizes a corresponding number of tlmes and at each deenergizationbreaks the circuit of relays 210 and 211 of the repeater E. Whence itwill be seen that relays 210 and 211 will be decnergized a number oftimes corresponding to the first digit of the called numb At the firstdeiinergization of relay 210, a circuit is completed for the slow actingre lay 214 as follows: ground atv G contact springs 217 and 216, contactsprings 238 and 237, and winding of relay 214 to battery B Relays 213and 214 being slow acting, re-

tain their armatures 1n operated position durlng impulses, after whichrelay. 214 retracts its armature. Inits. energized; condition,

relay, 214 disconnects the conductors 243 from the conductors 240 and241,. respectlvely, and from the normally bridged 24.2 and coil 215;substitutes for the lattera direct I path by way of contact springs 220and 219 and contact springs 230 and 229; and com- .pletes an initialenergizing circuit for relay 212 as follows': ground at G, winding ofrelayr212, and contactsprings 227 and 228 to'battery 13 Relay 212 looksitself in an obvious manner by closing contact springs 221 and 222; andalso, by separating contact springs 223 and 224, opens the circuit bytheline drop 162 (M Fig.3).

Relay 211, at each deenergization, breaks the circuit of the line relay250 of the selector F; In response to these interruptions of itscircuit, the line relay 250 is deenergized a corresponding number oftimes and sends at eachdeenergization' an impulse from ground at C tothe slow acting relay 252 and the vertical magnet 255 in series. Thevertical magnet, in response to these impulses, steps up the shaft untilthe wipers stand opposite the horizontal level which contains terminalsoftrunk lines extending to the desired group. The relay 252, being slowacting, retains its armature during the series-of impulses and closes acircuit for the test rela 254, which latter relay, upon attracting 1tsarmature, locks itself to ground at G" and also prepares a circuit forthe: rotary magnet 256. At the end of the series of impulses the relay252 deenergizes, thereby closing the aforementioned rotary magnetcircuit, whereupon the wipers 260,

261 and 262 start rotating in search of an idle trunk line. As is wellknown, the ro tary magnet interrupts its own circuit and also'thelocking circuit of the test relay254 at every energization, the contactsin the latter circuit, however, being short-circuitedthe test or privatewiper 261 while passlng over busy or grounded test contacts. As soon,therefore, as the test wiper reaches an ungrounded test contact thearmature of test relay 254 falls back and opens the rotary magnetcircuit, thereby bringing the wipers to rest upon the contacts of anidle trunk line, assumed to be in this case thecontacts 263, 264, and265. Upon deergizing, completes a holding circuit for the line switchingrelay 253 of the. selector F over the. 'l'ollowing path: ground at G,contact springs 320, bank contact 264, wiper 2131. contact springs ofrelay 251, and windingot" relay 253 to battery B The operator at the No.1 exchange may now manipulate her calling device S in accordante withthe. last two digits of the desired mnnber, resulting now in two seriesof ileiaiergizations of the .line relay 300 of the connector ll. Underthe control of the line relay 300, the wipers 321, 322, and 323 areraised by the vertical magnet 307 and rotated by the rotary magnet 308until they arrive at contacts which are terminals of the line ofsubstation A. After each series of impulses the private magnet 311 iscontrolled through the medium of the slow acting relay 302 (in serieswith the operating magnets). whereby the side switch wipers 312. 313.314, and 315 are advanced first to second position and finally to thirdposition (it being assumed that the line of substation was idle whencalled).

As side switch wiper 315 comes into its third position, a circuit iscompleted from ground at (1 by way of wiper 322 and bank contacts 325 tothe holding winding 330 of line switch t". Upon energizing, the holdingwinding operates the cut-off armature 331. whereby the line conductorsof substation A are disconnected from their connections in line switchC. Ground from (l also extends to multiple contacts similar to contact325 in the banks of other connectorsof the group, thereby making theline busy to other calls. By the advance of side switch wipers 312 and313 to their third positions the connection is completed to the calledline, relay 304 being denergized. By the advance of side switch wiper314 to its third position a circuit is completed for the ringing relay303, which is operated intermittently thereafter by the interrupter I tosignal the. subscriber at substation A. \Vhen the called subscriberremoves his receiver in response to the ringing of his bell a circuit iscompleted in the well known manner for the double wound back bridgerelay 309 (ringing relay 303 being temporarily deenergized) which relay,upon energizing, reverses the incoming line conductors (of no particularconsequence) and also completes a circuit for the ring cut oil relay305. The ring cut-01f relay, upon attracting its armature, locks itselfto ground at (F and at the same time opens the circuit of the ringingrelay 303.

At the No. 1 exchange, when the operator has completed the dialing ofthe required number she may restore the calling device key K, therebymaking the calling device S available for use in other connections. Theconnection with substation A may be completed at once or the operatormay wait for the response of the called subscriber, the method adopteddepending ordinarily upon whether it is only required to connect with a.certain substation in the No. 2 exchange or whether a certain particularperson there is wanted. Assuming the latter to be the case, the operatorfirst ascertains that the proper person is at the telephone in thedistant exchange, then inserts the answering plug of the cord circuit Pin jack J, and operates the ringing key K. By the insertion of the plugin jack J, a circuit is completed which may be traced from ground at Gby Way of low resistance sleeve relay 35, sleeve of plug, sleeve of jackJ, conductor 16, and cut-ofi' winding 48 of line switch C to battery B.The cut-ofl' armature 49 is thereby operated to disconnect the lineconductors 12 and 13 from their connections in line switch C. A branchof the above circuit extends over conductor 20 to multiple contacts inthe banks of connector switches having access to the line of substationA through the medium of normal conductors 21 and 22, thereby making theline of substation A busy to incoming automatic calls.

In response to the ringing of his bell the calling subscriber atsubstation A may now remove his receiver from the hook, when therequired connection will have been completed. Current for thetransmitter at the calling substation is supplied through the windingsof the supervisory relay 36 of the cord circuit P, while current for thetransmitter of the called substation is supplied through the windings ofthe double wound back bridge relay 309 of the connector H. The completepath for voice currents has been drawn in heavy lines and should beapparent without further explanation.

When the conversation is finished both subscribers will replace theirreceivers. Upon replacing the receiver at substation A the relay 36 isdeenergized, thereby lighting the supervisory lamp L. By this means theoperator is informed that the conversation is at an end, whereupon shemay remove both plugs of cord circuit P from the jacks. The removal ofthe plug from jack J removes ground from conductor 16, wherebytheindividual apparatus associated with substation A is restored to normalcondition. The removal of the plug from jack J breaks the circuit ofrelay 50 Fig. 2). Relay 50, upon (leenergizing, breaks the lockingcircuit of relay 51, which relay, upon deenergizing in turn, disconnectsthe generator 80 from the circuit of the A. C. relay 152 (Fig.

3). The relay 152 thereupon retracts its armature and breaks the circuitof relays 210 and'211 of repeater E. By the (lechergization of relay 211the circuitof the line relay 300 of the connector H is broken,

whereupon all the automatic switches are restored to normal position inthe well known manner.

If the line of substation A had been busy when called, the connector Hwould have operated after the final series of impulses to connect a leadfrom the busy signaling machine Q with one side of the calling line, theside switch Wipers being held in the second position for this purposeand to prevent connection with the called line. Upon perceiving the busysignal, the operator at the distant exchange removes the plug from jackJ 4 whereupon the apparatus is restored to normal as hereinafterdescribed.

It is thought that the description which has been given will render theoperation clear without further details. It should be mentioned.however, that the toll circuits shown in Figs. 2 and 3 are two way, i.6., connections may be established in either direction. Since theequipment at one exchange is an exact duplicate of that at the otherexchange, the manner of establishing a connection in the reversedirection will be l sufficiently obvious.

nections is absolutely prevented.

ation is well known. Assuming that the operator at the No. 1 exchangedesires to establish a connection manually with the aid of the operatorat the U0. 2 exchange, she will use the same cord circuit as before, butinstead of throwing the calling device key K she will operate theringing key K in her cord circuit. As a result, the drop 162 at thedistant exchange is actuated, thereby signaling the operator at the No.2 exchange, who will respond by inserting the plugof a cord circuitsimilar to cord circuit l in jack J The operators at the two exchangesnow converse or establish a connection between local subscribers intheir respective exchanges as desired. Interferenz e between manual andautomatic con- \Vheneyer a plug is inserted in the jack of an idle tollline, the drop and the automatig v repeater associated therewith arediscomnected. Conversely, whenever the repeater is operated from thedistant end, a busy potential is placed on the sleeve of the jack andthe cut-off relay is disabled, all as has been described. It isimportant to note in this connection that while the operator at the No.2 exchange cannot interfere with automatic connections establishedbyoperators in the No. 1 exchange to the extent of disconnecting suchconnections, she is enabled, nevertheless, to supervise such a onnectionby simply disregarding the busy test and plugging into the jack. Thisfeature is often a valuable one.

][ will now describe briefly an alternative method of carrying out minvention, or more accurately, a modification of the same. For thispurpose Figs. 2 and 3 should be removed from the layout and Figs. 25 and3 substituted therefor. The arrangement shown in Figs. 2 and 3 andalready described may be termed a parallel arrangement, for the A. C.relays at each exchange are included in three parallel branches of thesimplex operating circuit. The arrange ment shown in Figs. 2 and 3diflers chiefly from the previous one in that itis a series arrangement,the A. C. relays at each ex change being all connected in series. Aconsiderable portion of the apparatus shown in Figs. 2 and 3 is the sameas the corre-' sponding parts in Figs. 2 and 3 and some of suchapparatus has accordingly been in dicated by the same numerals.

As in the parallel arrangement the generators 80 and 180 deliver currentof one frequency; generators 81' and 181 deliver current .of anotherfrequency; while generators 82 and 182" deliver current of still anotherfrequency. No barriers are used in connection with the A. C. relays butthe. operation of these relays depends on local resonance. Morespecifically relay 152' (Fig. 3 is so designed that its local circuitincluding the two windings and the condenser in series will be resonantto the frequency of generator 80 (Fig. 2 The remaining A. C. relays arelikewise so constructed that local resonance will occur with the properfrequency. A further requirement in the design of the A. C. relays isthat they should have very low resistance in order that the localcurrents produced when resonance occurs will be much greater than theline currents.

The operation briefly is as follows: When the key K is operated acircuit including generator 80 is closed over the following path: upperterminal of generator 80, contact springs and 66, contact springs 77 and76, calling device S, and primary winding of transformer T to the lowerterminal of generator 80. An alternating current is now induced in. .thesecondary winding of transformer T and takes the following path: groundat G, A. C. relay 52, secondary winding of transformer T, A. C. relay53', secondary winding of transformer T, A. C. relay 5 secondary windingof T the simplex operating circuit to the No. 2 exchange, winding oftransformer T, A. C. relay 1%, secondary winding of transformer TflA. C.relay 153, secondary winding oftransformer T and A. C. relay 152' toground at G It will be noticed that the primary windings of thetransformers T, T etc., are short circuited so that the secondarywindings offer little impedance to current flow in the above circuit. 1

In. response to current flow in the above circuit, relays 52 and 152'attract their armatures. The operation of these relays is not directlydue to the current in the line but is due principally to the localcurrents set up in the local circuits; for, it will be remembered, theserelays are so constructed that resonance occurs with the frequency ofcurrent delivered by generator 80. The remaining A. C. relays, sincetheir local circuits are out of tune with the frequency of current nowon the line, are not operated, the retractile springs of their armaturesbeing so adjusted that three or four times the line current produced byany one of the generators is required to overcome their tension.

It will be clear now that by operating the calling device Sinterruptions may be produced in the primary circuit of transformer T,whereby an interrupted alternating current is produced in the secondarywinding and in the operating circuit including A. C. relay 152 at thedistant exchange. The A. C. relay 152 is adapted to control theautomatic switches shown in Figs. 4 and 5 through the medium of repeaterE (Fig. 4:) whereby the required connection can be establishedsubstantially as previously de scribed. v

It will be seen from the foregoing that my invention provides a simpleand efficient method by which a plurality of automatic switches may becontrolled simultaneously over a single circuit through the medium ofsuperimposed alternating currents of different frequencies, togetherwith tuned alternating current relays responsive thereto.

While I have found it convenient, in explaining my invention, to show acertain specific embodiment thereof, I do not wish to limit myself tothe precise forms shown, for modifications will no doubt be devised bypersons skilled in the art. I desire, therefore, to include and haveprotected by Letters Patent all forms and modifications of my inventionwhich may come within the scope of the appended claims.

What I claim as my invention is:

1. In combination, a circuit, a plurality of sources of current ofdifferent frequency, a plurality of relays in said circuit, a localcircuit for each relay tuned for resonance to a particular frequency ofcurrent, and an automatic trunking switch associated with each relay, aseries of line terminals for each switch arranged in a bank at eachswitch, lines terminating in said terminals, an impulse sending deviceassociated with each source of alternating current and each providedwith means for sending impulses from its associated source to operatethe corresponding relay over said circuit to operate the correspondngtrunking switch to establish a connection with any one of said lines insaid series.

2. In combination,- a circuit, a plurality of sources of current ofdifferent frequency, a plurality of relays in said circuit, each relayhaving two windings connected in parallel to form a closed loop, acondenser in each loop whereby the several loops are each madeelectrically resonant to a different frequency of current, an automatictrunking switch associated with each relay, a series of line terminalsfor each switch arranged in a bank at each switch, lines terminating insaid terminals, an impulse sending device associated with each source ofalternating current and each provided with means for sending impulsesfrom its associated source to operate the corresponding relay over saidcircuit to operate the corresponding trunking switch to establish aconnection with any one of said lines in said series.

3. In combination, a plurality of circuits, a conductor common to saidcircuits, a source of current in each circuit, said sources deliveringalternating currents of different frequency, a relay in each circuit, acapacity and an inductance in each circuit, whereby each circuit istuned to the frequency of the current source included therein, and alocal circuit for each relay including the windings of the relay and acondenser, each local circuit adjusted for resonance to the samefrequency as its associated main circuit, an automatic trunking switchassociated with each relay, a series of line terminals for each switcharranged in a bank at each switch, lines terminating in said terminals,an impulse sending device associated with each source of alternatingcurrent and each provided with means for sending impulses from itsassociated source to operate the corresponding relay over said circuitto operate the corresponding trunking switch to establish a connectionwith any one of said lines in said series.

4. In combination, a plurality of circuits, a conductor common to saidcircuits, a source of current in each circuit, said sources deliveringalternating currents of different frequency, a relay in each circuit, acapacity and inductance in each circuit associated with the currentsource included therein, a capacity and inductance in each circuitassociated with the relay included therein, whereby each circuit istuned to the frequency of its associated current source, and a localcircuit for each relay including the windings of the relay and acondenser, each local circuit adjusted for resonance to the samefrequency as its associated main circuit, an automatic trunking switchassociated with each relay, a series of line terminals for each switcharranged in a bank at each switch, lines terminating in said terminals,an impulse sending device associated with each source of alternatingcurrent and each provided with means for sending impulses from itsassociated source to operate the corresponding relay over said circuitto operate the corresponding trunking switch to establish a connectionwith any one of said lines in said series.

. 5. In combination, a plurality of circuits,

a conductor common to said circuits, a

windings of the relay and a condenser, each local circuit adjusted forresonance to the same frequency as its associated main circuit, anautomatic trunkin switch associated with each relay, 2, series of lineterminals for each switch arranged in a bank at each switch, linesterminating in said terminals, an impulse sending device associated witheach source of alternating current and each provided with means forsending impulses from its associated source to operate the correspondingrelay over said circuit to operate the corresponding trunking switch toestablish a. connection with any one of said lines in said series.

6. In combination, a circuit, a plurality of sources of alternatingcurrent of different frequency, a plurality of parallel branches of saidcircu t, a relay 1n each branch, means for electrically tuning saidbranches whereby the relays included therein are each made responsiveonly to a particular frequency of current 'in said cir cuit, and a localcircuit for each relay including the windings of the relay and acondenser, each local circuit adjusted for resonance to the samefrequency as its associated main circuit, an automatic trunking switchassociated with each relay, a series of line terminals for each switcharranged in' a bank at each switch, lines terminating in said terminals,an impulsesending device associated with each source of alternatingcurrent and each rovided with means for sending impulses rom itsassociated source to operate the corresponding relay over said circuitto operate the .cor-

responding trunking switch to establish a connection with any one ofsaid lines in said series. I

7 In a telephone system, a 'lurality of automatic progressively movab eswitches, controlling circuits for said switches having a commonconductor, a source of current in eat-la circuit, saidsources deliveringcurrents of different electrical character, and a controlling relay ineac circuit for the associated switch, said relays each responsive onlyto current from the particular source included in the same circuit.

8. In a telephone system, a plurality of automatic progressively movableswitches, controlling circuits for said switches having a commonconductor, a source of current in each circuit, said sources deliveringalternating currents of difi'erent frequency, and a controlling relay ineach circuit for the associated switch, said relays each responsive onlyto current of a particular frequency.

9; In a telephone system, a plurality of automatic progressively movableswitches, controlling circuits for said switches having a commonconductor, a source of current in each circuit, said sources deliveringalternating currents of diderent frequency, a controlling relay in eachcircuit for the associated switch, and a capacity and an inductance ineach circuit, whereby each circuit is tuned to the frequency of thecurrent source included therein.

10. In a telephone system, a plurality of circuit for each relayincluding the windings of the relay and acondenser, each local circuitadjusted for resonance to the same frequency as its associated maincircuit.

11. In a telephone system, a plurality of automatic progressivelymovable switches, controlling circuits for said switches having a commonconductor, a source of cur rent in each circuit, said sources deliveringalternating currents of different frequency, a controlling relay in eachcircuit for the associated switch, said relays each responsive only tocurrent of a particular frequency, and a local circuit for each relayincluding the windings of the relay and a condenser, each local circuitadjusted for resonance to the same frequency as its associated maincircuit.

12. In a telephone system, a plurality of automatic progressivelymovable switches,

13. In a telephone system, a plurality of automatic progressivelymovable switches, a common controlling circuit for said switches, aplurality of branches of said circuit corresponding in number to thenumber of said switches, a relay in each branch for ,controlling aparticular switch, a plurality of sources of alternating current ofdifferent frequency, means for separately including said sources in saidcircuit, and means for directing the current from each source through aparticular branch, whereby said switches may be operated independentlythrough the medium of their controlling relays.

14. In a telephone system, a plurality of automatic progressivelymovable switches, a common controlling circuit for said switches, aplurality of branches of said circuit corresponding in number to thenumber of said switches, a relay in each branch for controlling aparticular switch, a source of alternating current corresponding to eachrelay, said sources delivering currents of different frequency, aninductance and a capacity in each branch, whereby each branch is tunedto the frequency of the corresponding source, and means for includingsaid sources separately or simultaneously in said circuit to operate thecorresponding relays.

15. In an automatic telephone system, a first exchange, a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said first lines, an automatic switch at the secondexchange for each of said lines, a common controlling circuit for saidswitches superimposed on said phantom line, means at the first exchangefor transmitting alternating cur rents of different frequencies oversaid controlling circuit, and controlling relays for said switches insaid circuit at the second exchange, each of said relays responsive onlyto current of a particular frequency.

16. In an automatic telephone system, a first exchange, a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said first lines, an automatic switch at the secondexchange for each of said lines, a common controlling circuit for saidswitches superimposed on .said phantom line, means at the first exchangefor transmitting alternating currents of different frequencies over saidcon trolling circuit, a plurality of branches of said cont-rollingcircuit at the second exchange, each branch containing a relay forcontrolling a particular one of said switches, and means in each branchwhereby said relays are each made responsive only to current of aparticular frequency.

17. In an automatic telephone system, a first exchange, a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said first lines, an automatic switch at the secondexchange for each of said lines, a common controlling circuit for saidswitches superimposed on said phantom line, means at the first exchangefor transmitting alternating currents of different frequencies over saidcontrolling circuit, controlling relays for said switches in saidcircuit at the second exchange, each of said relays responsive only tocurrent of a particular frequency, and means at said first exchange forintermittently interrupting the transmission of any of said currents,whereby said switches may be operated through the medium of theircontrolling relays.

18. In an automatic telephone system, a first exchange, a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said first. lines, an automatic switch at the secondexchange for each of said lines, a common controlling circuit for saidswitches superimposed on said phantom line, means at the first exchangefor transmitting alternating cur rents of difl'erent frequencies oversaid con trolling circuit, a plurality of branches of said controllingcircuit at the second exchange, each branch containing a relay forcontrolling a particular one of said switches, means in each branchwhereby said. relays are each made responsive only to current of aparticular frequency, and means at said first exchange forintermittently interrupt.- ing the transmission of any of said currents,whereby said switches may be operated through the medium of theircontrolling relays.

19. In an automatic telephone system, a first exchange and a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said lines, a manual jack for each line in eachexchange, an

automatic switch for each line at the second exchange, a controllingcircuit for said switches superin'iposed on said phantom line, sourcesof alternating current of different frequency at the first exchange,controlling relays for said switches in said circuit at the secondexchange, each of said relays responsive only to current of a particularfrequency, means for including said sources separately or simultaneouslyin said circuit, and means for intermittently interrupting the flow ofcurrent from any source so included whereby to operate the correspondingswitch at the second exchange.

20. In an automatic telephone system, a first exchange and a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said lines, a manual jack for each line in eachexchange, an automatic switch for each line at the second exchange, acontrolling circuit for said switches superimposed on said phantom line,sources of alternating current of different frequency at the firstexchange, controlling relays for said switches in said circuit at thesecond exchange, each of said relays responsive only to current of aparticular frequency, means for including said sources separately orsimultaneously in said circuit, means for intermittently inter 'uptingthe flow of current from any source so included whereby to operate thecorresponding switch at the second exchange, and a cut-off relay foreach line in the second exchange, each relay operated when manualconnection is made with its associated line to disconnect the associatedswitch.

21. In an automatic telephone system, a first exchange and a secondexchange, a pair of lines connecting said exchanges, a phantom linesuperimposed on said lines, a manual jack for each line in eachexchange, an automatic switch for each line at the second exchange, acontrolling circuit for said switches superimposed on said phantom line,sources of alternating current of different frequency at the firstexchange, controlling relays for said switches in said circuit at thesecond exchange, each. of said relays responsive only to current of aparticular frequency, means for including said sources separately orsimultaneously in said circuit, means for intermittently interruptingthe flow of current from any source so included whereby to operate thecorresponding switch at the second exchange, and means associated witheach switch for placing a busy potential upon the sleeve of the jackassociated with the same line at the same exchange when such switch isoperated.

22. In an automatic telephone system, a pair of lines connecting twoexchanges, a phantom line superimposed thereon, a manual jack for eachline at each exchange, an automatic switch for each line at eachexchange, a controlling circuit for said switches superimposed on saidphantom line, a source of current for each line at the first exchange,said sources delivering alternating currents of different frequency,similar sources for said lines. at the other exchange, a controllingrelay in said circuit for each of said switches at the first exchange,said relays each responsive only to current of a particular frequency,similar controlling relays for the switches at the other exchange, meansat each exchange for including the current sources thereat separately orsimultaneously in said circuit, and means for intermittentlyinterrupting the flow of current from any source so included whereby tooperate the corresponding switch at the other exchange.

23. In an automatic telephone system, a pair of lines connecting twoexchanges, a phantom line superimposed thereon, a manual jack for eachline at each exchange, an automatic switch for each line at eachexchange, a controlling circuit for said switches superimposed on saidphantom line, a source of current for each line at the first exchange,

said sources delivering alternating currents of different frequency,similar sources for said lines at the other exchange, a controllingrelay in said circuit for each of said switches at the first exchange,said relays each responsive only to current of a particular frequency,similar controlling relays for the switches at the other exchange, meansat each exchange for including the current sources thereat separately orsimultaneously in said circuit, means for intermittently interruptingthe flow of current from any source so included whereby to operate thecorresponding switch at the other exchange, and means associated witheach switch for placing a busy potential upon the sleeve of the ackassoclated with the same line at the same exchan e when such switch isoperated.

24:. In com ination, a plurality of sources of current of differentfrequency, a plurality of relays each having two windings, a maincircuit including all of said relays in series and the two windings ofeach relay in parallel, means for including said sources separately insaid circuit, none of said relays being directly responsive to theresulting current flow in the main circuit, and a closed local circuitfor each relay including its two windings and a condenser of suchcapacity that the associated local circuit is made resonant to thefrequency of a particular one of said current sources, whereby when anyparticular current source is included in the main circuit, localcurrents of greater value than the current in the main line will becaused to flow in the corresponding local circuit in order to operatethe associated relay.

25. In a telephone system, a plurality'of automatic trunking switches, aseries of line terminals for each switch arranged in a bank at eachswitch,lines terminating in said terminals, in combination with aplurality of sources of alternating current of different frequencies anda plurality of relays, a line common to said sources and relays, animpulse sender for each source of alternating current for sendingimpulses from its associated source over said common line to operate thecorresponding relay, said relays being tuned each to respond to only oneof the frequencies of said sources and each to a different one, and eachrelay having control of a different one of said automatic trunkingswitches whereby said switches may be operated by said calling devicesone at a time or more than one at the same time without the impulsesfrom one calling device and source interfering with the impulses fromanother calling device and source.

26. In a telephone system, a plurality of automatic trunking switches, aseries of line terminals for each switch arranged in a bank at eachswitch. lines terminating in said terminals. in combination with aplurality of sources of alternating current of different frequencies anda plurality of relays, a line common to said sources and relays, animpulse. sender for each source of alternating current for sendingimpulses from its associated source over said common line to operate thecorresponding relay, said relays being tuned each to respond to only oneof thefrequencies of said sources and each to a different one, and eachrelay having control of a different one of said automatic trunkingswitches whereby said switches may be operated by said calling devicesone at a time or more than one at the same time without the impulsesfrom one calling device and source interfering with the impulses fromanother calling device and source, each relay having two windingsconnected in multiple, the two multipled windings of each relayconnected in series with a portion of said common line, sald multipledwindings of each relay forming a local closed series circuit.

27. In a telephone system, a plurality of automatic trunking switches, aseries of line terminals for each switch arranged in a bank at eachswitch, lines terminating in said terminals, in combination with aplurality of sources of alternating current of different frequencies anda plurality of relays, a line common to said sources and relays, animpulse sender for each source of alternating current for sending"limpul'ses from its associated source over said common line to operatethe corresponding relay, said relays being tuned each to respond to onlyone of the frequencies of said sources and each to a different one, andeach relay having control of a different one of said automatic trunkingswitches whereby said switches may be operated by said calling devicesone at. a time or more than one at the same time without the impulsesfrom one calling device and source interfering with the impulses fromanother calling device and source, each relay having two windingsconnected in multiple, the two multipled windings of each relayconnected in series with a portion of said common line, said multipledwindings of each relay forming a local closed series circuit, and acondenser in said local closed circuit.

28. In a telephone system, a circuit, a source of alternating currentand a reactance connected in series in said circuit, a relay, said relayhaving two windings connected in multiple with each other and the twomultipled windings connected in series in said circuit with said currentsource and said reactance, said relay multipled windings forming a localclosed series circuit tuned to the frequency of current from saidsource,

another circuit controlled by said relay, an impulse calling device forsending impulses over said first circuit from said source of current forcontrolling said relay, an automatic trunking switch, a series of linesterminating in a bank at said switch, said switch controlled by saidrelay over said circuit to extend a connection to any one. of saidlines.

29. In a telephone system, a circuit, a source of alternating currentand a reactauce connected in series in said circuit, a relay, said relayhaving two windings connected in multiple with each other and the twomultipled windings connected in series in said circuit with said currentsource and said reactance, said relay multipled windings forming a localclosed series circuit having a'condenser included therein tuned to thefrequency of current from said source, another circuit controlled bysaid relay, an impulse calling device for sending impulses over saidfirst circuit from said source of current for controlling said relay, anautomatic trunking switch, a series of lines terminating in a bank atsaid switch, said switch controlled by said relay over said circuit toextend a connection to any one of said lines.

30. In a telephone system, a circuit, a source of alternating current, arelay, said relay having two windings connected in multiple with eachother, thetwo multipled windings connected in series in said circuit,said relay multipled windings forming a local closed series circuittuned to the frequency of current from said source, another circuitcontrolled by said relay, an impulse sending device for sending impulsesover said first circuit from said source of alternating current forcontrolling said relay, an automatic trunking switch, a series of linesterminating in a bank at said switch, said switch controlled by saidrelay over said circuit to extend a connection to any one of said lines.

31. In a telephone system, a circuit, a plurality of sources ofalternating current associated therewith, each source producing acurrent of different frequency, a plurality of relays associated withsaid circuit, each 1!- la v having two windings connected in multiple,and the two multipled windings of each relay connected in series with aportion of said circuit, said multipled windings of each relay forming aclosed series circuit. each of which is tuned to a particular one of thefrequencies produced by said sources, each of said relays controllinganother circuit, an impulse sending device associated with each one ofsaid sources of alternating current whereby impulses from any or all ofsaid sources may be transmitted over said first circuit to said relaysfor controlling said relays, an automatic trunking switch in each one ofthe circuits controlled by each one of said relays, a difierent seriesof lines terminating in a bank at each one of said switches, each ofsaid switches controlled :by its assoclated relay over the relaycontrolled by said circuit to extend a connection to any one of saidlines.

32. In a telephone system, a second exchange, a pair of lines connectingsaid exchanges, a phantom line superimposed on said first lines, anautomatic switch at the second exchange for each of said lines, a commoncontrolling circuit for said switches superimposed on said phantom line,means at the first exchange for transmitting currents of differentcharacters over said controlling circuit simultaneously, and meansresponsive to said currents at the second exchange for operating saidswitch at the same instant independently of each other.

33. In a telephone system, a first exchange, a second exchange, a plairof lines connecting said exchanges, a p antom line superimposed on saidfirst lines, an automatic switch at the second exchange for each of saidlines, a common controlling circuit for said switches superimposed onsaid phantom line, operator controlled means at the first exchange forintermittently transmitting currents of different characters over saidcontrolling circuit simultaneously, and a plurality of relays at thesecond exchange responsive to a first exchange,

said currents one for each particular char- I actor of current, wherebythe said switches are operated at the same instant independently of eachother.

34. In a telephone system, a first exchange, a second exchange, a plairof lines connecting said exchanges, a p antom line superimposed on saidfirst lines, an automatic switch at each exchange for each of saidlines, a common controlling circuit for said switches superimposed onsaid phantom line, means at each exchange for transmitting a pluralityof currents of different characters over said controlling circuitsimultaneously, and means responsive at the second exchange to saidcurrent of one character and at the first exchange to said currents of adifferent character, for operating one of the said switches associatedwith each of said lines at the same instant independently of each other.

35. In combination with a talking circuit established betweentelephones, Whlch talking circuit has two parallel talking paths, asecond circuit, one side of said second circuit having three sections inseries, one of said sections having in multiple the parallel sides ofsaid talking circuit, another one of said sections having an alternatingcurrent generator, and the third of said sections having an alternatingcurrent relay, said relay controlling the continuity of said talkingcircuit, said relay maintained energized by current from saidalternating current generator while the conversation is going on betweensaid two telephones for malntaining the continuity of the talkingcircuit.

Signed by me at Chicago, Cook county, State of Illinois, this 19th dayof April,

ARTHUR BESSEY SMITH.

